The present invention relates to magnetoresistive sensors. In particular, the present invention relates to a magnetoresistive sensor having fewer than four terminals.
Magnetoresistive sensors are used in magnetic storage systems to detect magnetically encoded information. A changing magnetic field modulates the resistivity of the magnetoresistive sensor. The resulting change in resistance is detected by passing a sense current through the magnetoresistive sensor and measuring the voltage drop across the magnetoresistive sensor. The resulting voltage signal can be used to recover information from a magnetic storage medium such as a magnetic disk.
Practical magnetoresistive sensors are typically formed using ferromagnetic metal alloys, for example, nickel iron (Ni.sub.80 Fe.sub.20). The nickel iron alloy is deposited in a thin film upon a substrate or wafer. Changing magnetic fields in a magnetic storage medium produce changes in the magnetization of the magnetoresistive sensor and thereby change the resistance of the sensor.
As many as four electrical connections to the magnetoresistive sensor are needed to use the head readback stored information. Two connections are used to supply electrical current through the sensor, and two other connections are used to detect changes in voltage across an active region of the head due to the change in resistance associated with the presence of a magnetic field near the magnetoresistive sensor. Detection circuitry is connected to the magnetoresistive sensor so that the changing resistance of the magnetoresistive sensor can be monitored to produce an output which is representative of information stored on the magnetic storage medium.
The overriding goal of all magnetoresistive sensor designs is to develop a device which is free from Barkhausen noise. This is achieved using the "hammerhead" design described in U.S. Pat. No. 4,535,375 issued Aug. 13, 1985 to Mowry et al entitled "Magnetoresistive Head" which is incorporated by reference. The magnetoresistive head of the Mowry et al patent uses a tapped "barber pole" array.
The barber pole array develops a longitudinal magnetic field to stabilize a central single domain region and thereby eliminate the possibility of signal degradation due to Barkhausen noise. This structure provides reproducible, stable magnetoresistive sensors. Four electrical connections are needed to operate the "Hammerhead" magnetoresistive sensor. Additionally, an integrated inductive write/magnetoresistive read head requires at least two additional leads for a write coil. Therefore, an integrated inductive write/magnetoresistive read head using the hammerhead design requires a minimum of six electrical connections.
A magnetoresistive head which requires fewer connections to the magnetoresistive element, while maintaining the single domain integrity of the sensor, would improve reliability, decrease manufacturing costs and be a significant contribution to the art of magnetoresistive heads.